Internal combustion engines combust an air and fuel mixture to generate drive torque. More specifically, air is drawn into the engine and is mixed with fuel. The air and fuel mixture is combusted within cylinders to drive a crankshaft, producing drive torque. Mass airflow into the engine and the quantity of fuel injected determine the amount of drive torque generated.
Some engines include exhaust gas recirculation (EGR) systems to improve engine operation and reduce engine emissions. The EGR system includes an EGR valve that regulates an amount of exhaust gas that is circulated back to the intake manifold to be mixed with the air and fuel. The additional exhaust gas affects the amount of engine air intake through the throttle.
One traditional method of controlling engine air intake includes closed-loop EGR valve control and open loop throttle control. The desired throttle position is scheduled based on an open-loop look-up table. The EGR valve is controlled to regulate the mass airflow into the engine. In order to guarantee the set point can be reached under different conditions, the throttle must close more than is necessary, which results in reduced fuel economy due to excessive throttling.
Another traditional method uses closed-loop control of both the EGR valve and the throttle. The EGR valve and the throttle are controlled sequentially. In the low end of the control authority, where EGR valve itself is sufficient to achieve the intake air set point, only the EGR valve is active, which regulates the airflow to the target value while the throttle is fully open. At the high end of the control authority, where the EGR valve by itself is not sufficient to achieve the desired mass airflow, the EGR valve is fully open and the throttle is actuated. This strategy solves the problem of unnecessary throttling, however, it requires a high precision intake throttle valve and position sensor to accurately control the mass airflow.